The present invention relates to silicone compositions and more particularly the present invention relates to silicone compositions for treating gypsum paper to make it water repellent.
Gypsum board is well-known. Generally, gypsum board is formed by first forming the gypsum paper in paper making machines which is manufactured by driving the plies through a sizing bath which may contain alum and/or rosin for sizing the gypsum paper whereupon then the gypsum paper is formed to the desired thickness and collected off the end of the machine. Then in the manufacture of the gypsum board, the sheets of the gypsum paper are taken and there is put gypsum mixture between the sheets and the sandwich composite of gypsum paper with gypsum mixture is then semi-dried and cut to the appropriate lengths. The cut lengths of gypsum board are then put into a high temperature kiln where the final drying of the gypsum board is carried out prior to the shipping of the gypsum board composite.
There are several problems associated with the manufacture of gypsum board. First of all, when the gypsum mixture is first applied to the paper, some of the gypsum mixture migrates into the paper and crystallizes in the paper upon curing. One effect of this, is that the paper absorbs some of the water that is in the gypsum mixture and accordingly, the core of the gypsum mixture crystallizes and cures to a different crystalline mixture then the gypsum mixture at other parts of the cross section of the gypsum board. This phenomena is known as stratification and may result in weakening of the strength of the adhering of the gypsum paper to the gypsum core in the gypsum board. This stratification and weakening of the adherence of the gypsum paper to the gypsum core mixture necessitates the use of larger amounts of water in the gypsum mixture when the gypsum board is formed and accordingly, the result is longer drying times are needed for curing or completely drying the gypsum board before it is ready to be shipped. Accordingly, this results in additional expenses in the manufacture of such gypsum board which would desirably be eliminated.
Another problem that resulted from the absorption of large amounts of water by the paper from the gypsum mixture during the formation of the gypsum board was that the paper plies in the gypsum paper would be delaminated because of the excess water that was absorbed. This problem was overcome by the utilization of certain resins in the paper plies which would repell or counteract against the delamination effect of the water in the gypsum paper. However, this added to the expense of the overall production of the gypsum board.
Such effects were substantially eliminated or circumscribed considerably by the disclosure of Bieri et al U.S. Pat. No. 3,389,042 in which it is taught to treat the surface of one side of the gypsum paper with a hydrophobic silicone. The paper becomes water repellent and the paper may then be utilized, that is, that part of the side of the paper which is coated with the hydrophobic silicone, can be utilized to sandwich in between, gypsum mixture, without the resulting effects of stratification, and delamination as was experienced prior to the use of the silicones. The Bieri et al Patent discloses various types of silicone that may be utilized to treat gypsum paper, such as, expoxy functional polysiloxanes, methyl hydrogen polysiloxes, isocyanurate modified silanes and siloxanes and alkoxy functional silanes. In addition a product of a hydrogen silicone compound with a fatty acid ester, that is a poly ester polysiloxane block copolymer, is disclosed as a useful costing agent. Such silanes and siloxanes disclosed above and as set forth in the Bieri et al Patent were disclosed as being useful for the treating of gypsum paper in the formation of gypsum board so as to eliminate stratification, recalcination and delamination without the use of expensive additives or long drying times and as such were a general improvement over the prior art. However, there was a constant search to improve over the developments of the Bieri et al composition and processes.
One of these developments was the disclosure of Johnson et al U.S. Pat. No. 3,431,143, which discloses certain types of epoxy functional polysiloxanes for treating paper to it hydrophobic. The advantage of such epoxy functional polysiloxanes was that they tended to cure at a fast rate and they produce an excellent hydrophobic coat on the gypsum paper. In Johnson et al U.S. Pat. No. 3,511,699 the same expoxy functional polysiloxanes are disclosed for treating textiles as in the previous Johnson et al Patent. Accordingly, such silicones have found acceptance in the market place for utilization as water repellent treating agents for gypsum paper in the manufacture of gypsum board. However, there were several disadvantages with such silicone compounds.
First of all, the epoxy polysiloxanes while curing rapidly still did not cure at a sufficiently fast rate for the gypsum board manufacturing requirements. Thus, the gypsum paper that is treated with epoxy functional siloxanes had to be stored for a certain amount of time to allow the epoxy silicone to fully cure before the paper could be utilized to product gypsum board. In addition, it was desired to improve the hold down of the silicone on the gypsum paper and to improve the strength of the silicone film that was put on the gypsum paper. To do this, it was decided to try to include a filler and specifically a silicone filler along with the polysiloxane fluid. In accordance with this concept, various types of silica fillers were tried to be incorporated into the silicone fluid, which was used to treat gypsum board. Examples of such filler are colloidal fumed silica and colloidal precipitated silica.
Both of these silicas are reinforcing silicas, that, they increase the strength of the cured film that is formed. However, it should be noted that while reference is made to the fact that those silicon are colloidal fumed silica and colloidal precipitated silica, they are semi-dried colloidal silica particles in the state in which they are incorporated into silicone compositions which contains silanol groups on the surface of the particles. The term colloidal silica, as it will utilized in this case will refer to a liquid suspension of colloidal silica particles. However, such applications is fumed silica and precipated silica, which is stated previously, that such silicas when attempted to be incorporated into silicone compositions, made the silicone emulsion in which the silicone fluid was located unstable and very difficult to keep an emulsified form, and the fumed silica and the precipitated silica had a tendency to precipitate out of the emulsion.
Reference is also made to the Patent Application of William J. Raleigh Ser. No. 826,601 entitled "Silicone Compositions Useful As Textile and Paper Coatings", which is incorporated into the present case by reference, which discloses the use of a colloidal dispersion of silica which is a liquid suspension or dispersion of silica as a filler for a paper treating composition in which the base fluid is made by emulsion polymerization and in which the base fluid has vinyl groups and is cured by being reacted with a hydrogen polysiloxane in the presence of a platinum catalyst.
Such a composition is not the composition of the instant case. The instant composition does not contain platinum nor does it cure by the crosslinking of hydrogen groups onto vinyl groups of a base polymer so as to form a silicone film by SiH-olefin addition mechanism catalyzed by platinum. In addition, the Raleigh Application, as referred to above, discloses nothing about the use of that composition or any other composition for the treating of gypsum paper in the manufacture of gypsum board.
Accordingly, it is one object of the present invention to provide for a silicone composition for treating gypsum paper which cures in a very rapid fashion and cures more rapidly than an epoxy functional silicone.
It is an additional object of the present invention to provide a silicone composition for treating gypsum paper to make it water repellent which composition results in a silicone film of acceptional strength.
It is yet an additional object of the present invention to provide for a silicone composition for treating gypsum paper to make it water repellent wherein the silicone composition in the cure state has a better hold down to the gypsum paper and it imparts to the gypsum paper increased resistance to wetting.
It is still an additional object of the present invention to provide for a silicone composition for treating gypsum paper to make it water repellent wherein the silicone composition contains a liquid dispersion of colloidal silica. These and other objects of the present invention are accomplished by means of the disclosure set forth hereinbelow.